The present invention is related to cellular telephone systems in general and, more particularly, to a system and method for priority access channel assignment in a cellular telephone system.
Cellular telephone technology has evolved from relatively simple voice communication with limited geographical areas of coverage to sophisticated communication technology for voice communication, voice messaging, and data messaging virtually anywhere in the world. The number of mobile stations (i.e., users) has grown significantly in recent years. For example, in the United States, a large percentage of the population owns a cellular telephone. In other countries where there is no existing telephone system, cellular telephones are used in place of conventional telephone systems thus eliminating the need for physical wires from central switching offices to individual users.
The implementation of complex communication systems, such as described above, require communication standards and protocols that allow different organizations and manufacturers to maintain compatibility of the overall system. For example, many standards for cellular telephone communication have been established by the Telecommunications Industry Association (TIA) and the Electronic Industries Association (EIA). There are a number of TIA/EIA standards for cellular telephone communication. One such standard is TIA/EIA/IS-95-B, entitled xe2x80x9cMobile Station-Base Station Compatibility Standard for Dual-Mode Wide Band Spread Spectrum Cellular System.xe2x80x9d This standard, which may be referred to as IS-95-B, defines the communication protocol between mobile station and base station. The utilization of such a standard allows different manufacturers to construct equipment having different design features and implementations, but which will still function satisfactorily if it meets the standards set forth in IS-95-B.
Other features have been defined by TIA/EIA, but have no standards regarding implementation or protocol. For example, priority access channel assignment is a feature that allows a cellular system to prioritize incoming calls from mobile stations into assigned channels to the mobile stations based on these priorities. However, no protocol or standard exists to implement such a feature. Accordingly, it can be appreciated that there is a significant need for a communication protocol and standard that will allow priority access channel assignment. The present invention provides these and other features as will be apparent from the following figures and accompanying detailed description.
The present invention is embodied in a system and method for communication protocol for priority access channel assignment in a cellular telephone system. The protocol includes a first origination message transmitted from a first of the plurality of mobile stations to a first base station for a first call request from the first mobile station. The first origination message includes data indicative of a priority access channel assignment (PACA) request and a PACA origination element indicating that the first call request is initiated by the first mobile station. A service request message is transmitted from the first base station to a mobile switching center and includes PACA request data based on the PACA origination element transmitted in the first origination message. A PACA command message from the mobile switching center to the first base station indicates PACA authorization and a priority level associated with the first call request. A first PACA message is sent from the first base station to the first mobile station indicating that the first call request has been granted and placed in a queue associated with the first base station. The first PACA message also indicates the position of the first call request within the queue.
Additional protocol elements include a second PACA message to the first mobile station at a subsequent time when resources are available to process the first call request. The second PACA message contains data indicating that the first mobile station should reoriginate the first call request. In response to the second PACA message, the first mobile station transmits a second origination message including the PACA re-origination element set to a value indicating the re-origination of the first call request.
The protocol also includes various optional acknowledgment and confirmation messages that may be transmitted between the mobile station, the base station, and the mobile switching center. The first base station queue may contain a plurality of messages, each having an assigned priority level. The base station processes the pending calls in the queue based on priority with a higher priority pending call request being processed prior to a lower priority pending call request. In addition, the time of arrival of the call request is used to determine the position within the queue. For calls having identical priority levels, the base station processes calls that have the earliest time of arrival prior to processing calls having a later time of arrival.
If the mobile station moves from a first cell to a second cell and is now communicating with a second base station, the mobile switching center transmits a PACA query message to the first base station to request priority information from the first base station. The first base station transmits a PACA query acknowledgment in response to the PACA query message. The PACA query acknowledgment contains the requested priority information. Upon receiving the priority information from the first base station, the mobile switching center transmits a PACA command message to the second base station indicating PACA authorization and a priority level associated with the first call request. The second base station transmits a PACA message to the first mobile station indicating that the call request has been granted and placed in a queue associated with the second base station based on the priority level associated with the first call request.